npj: 二维材料杨氏模量的新测量方法—简便、精确、高空间分辨

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二维（2D）材料的弹性是其基本力学特性参量之一，对其器件应用及应变调控有重要影响。但要精确测量2D材料的弹性模量却难度不小，传统的悬空测量法还存在不少的不足之处。

来自中科院深圳先进技术研究院、南京航空航天大学和华盛顿大学的研究团队，开发了一种新方法，对于沉积在衬底上的2D材料，可直接高空间分辨地描绘其面内杨氏模量。以单层和多层MoS₂的为例，他们将双模态原子力显微镜（AFM）与有限元方法相结合，以测量AFM扫描探针针尖和样品之间的有效弹簧常数，同时兼顾区分衬底约束的影响。测定出的单层MoS₂的面内杨氏模量为265±13 GPa，较传统方法不确定性更低。不过双层MoS₂的面内杨氏模量与单层的面内杨氏模量却无法区分开来，对此他们用第一原理计算作了进一步验证。他们的这一方法，为支撑于衬底上的2D材料直接描绘其面内杨氏模量，提供了一种方便、稳健和准确的途径。

该文近期发表于npj Computational Materials 4:49 (2018)，英文标题与摘要如下，点击左下角“阅读原文”可以自由获取论文PDF。

Mapping the elastic properties of two-dimensional MoS₂ via bimodal atomic force microscopy and finite element simulation

Yuhao Li, Chuanbin Yu, Yingye Gan, Peng Jiang, Junxi Yu, Yun Ou, Dai-Feng Zou, Cheng Huang, Jiahong Wang, Tingting Jia, Qian Luo, Xue-Feng Yu, Huijuan Zhao, Cun-Fa Gao & Jiangyu Li 

Elasticity is a fundamental mechanical property of two-dimensional (2D) materials, and is critical for their application as well as for strain engineering. However, accurate measurement of the elastic modulus of 2D materials remains a challenge, and the conventional suspension method suffers from a number of drawbacks. In this work, we demonstrate a method to map the in-plane Young’s modulus of mono- and bi-layer MoS₂ on a substrate with high spatial resolution. Bimodal atomic force microscopy is used to accurately map the effective spring constant between the microscope tip and sample, and a finite element method is developed to quantitatively account for the effect of substrate stiffness on deformation. Using these methods, the in-plane Young’s modulus of monolayer MoS₂ can be decoupled from the substrate and determined as 265 ± 13 GPa, broadly consistent with previous reports though with substantially smaller uncertainty. It is also found that the elasticity of mono- and bi-layer MoS₂ cannot be differentiated, which is confirmed by the first principles calculations. This method provides a convenient, robust and accurate means to map the in-plane Young’s modulus of 2D materials on a substrate.

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